Radio receiver



, ATI'G/ O, Ba/2% I. O. BANKS RADIO RECEIVER Filed Oct. 24, 1936 r7.1@ ser GND.

DUT arm( April 4 Patented Apr. 4, 1939 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to signal volume control devices for radio receivers, and the primary object of the same is to improve the regulation characteristics of devices of this type.

5 Another object is to improve apparatus such as that disclosed in my Patent No. 2,047,092, for Radio antenna, issued July '7, 1936, wherein the effective tone volume of the radio receiver may be controlled by a pair of switches, one to ground lo either side of the input circuit with r without an outside antenna and the other to adjust the grounding by potentiometer means connected across said input circuit.

The foregoing and other objects and advantages l will become apparent in View of the following description taken in conjunction with the drawing, wherein- Figure 1 is a fragmentary circuit diagram of an input circuit illustrating my improved control 30 unit used as a signal input regulating means between an outside antenna and ground;

Figure 2 is a similar view but showing the unit coupled up with both an outside antenna and an auxiliary or indoor antenna;

i3 Figure 3 is a further circuit diagram showing the unit connected between the signal input and power supply circuits of a radio receiver;

Figure 4 is an exterior fragmentary view of a portion of a panel board with the improved control unit installed thereon;

Figure 5 is an enlarged interior View of the lower portion of Figure 4;

Figure 6 is substantially central transverse sectional view of the unit.

55 Referring to the drawing in detail, in Figure 1 a conventional input circuit is shown and includes a coupling A of the air core transformer type having its primary S connected between the antenna 'l and ground 8 through a resistance and control O device generally indicated at B and embodying the features of the present invention. The secondary 9 of the coupling is in multiple with a variable lcondenser II) and may, for example, be

connected between the ground and grid of a thermionic tube, not shown, forming part of the main radio circuit, also not shown herein since such showing is not essential to an understanding of the invention.

The structure of the control device B is shown 50 more or less in detail in Figures 4, 5 and 6 and comprises a resistance II which is attached to an insulated backing or supporting plate I2. A rotatable sliding contact member I3 is provided and is mounted on the inner end of shaft Il, member 55 I3 having as a part thereof a pair of arcuateshaped arms I3a and I3b which terminate in contacts I5 and I6, the latter being arranged in predetermined spaced relation and moving in unison when member I3 is rotated. At its one end, the resistance II is connected to a terminal Il which is shown in Figures 4 and 5 as being wired to the ground post I8 of the radio set, and at its opposite end said resistance is connected to terminal I9, which is wired to the antenna binding post 20. Shaft I4 is electrically connected to terminal 2| which is wired to the main or outdoor ground binding post 22.

Arms I3a and ISU have fixed thereon limit stops 23 and 24 which are adapted to contact an outwardly projecting contact member in the form of a pin 25 and limit the extreme positions of rotation or sliding contact of the contacts I5 and I6, such extreme positions being just short of actual contact with terminals I'I and I9.

A switch arm 26 is mounted on shaft I4 and is rotatable independently of the latter, said arm being provided with a contact head 26a, note dotted outline in Figure 4, adapted for selective engagement with terminals I 'I and I9 through electrical contacts 21 and 28 or adjustment to a neutral position between the latter.

Shaft I4 has secured on the outer end thereof a knob 29 having an indicating arrow 30 on the face thereof.

In Figure 1 the improved control unit is shown used as a potentiometer for adjusting the resistance between the main antenna I and ground 9, switch 26 being moved in electrical contact with terminal I'l, thereby grounding this terminal. Resistance I I for this purpose would be very high.

In Figure 2 the terminal I'I of the unit is connected through coil 3| with an auxiliary aerial 32. This latter aerial may be an indoor aerial or pickup device of any suitable type. Switch 26 is in neutral position in this instance so that both aerials I and 32 connect through resistance II and Contact member I3 with ground 3.

In Fig. 3 the improved unit is shown installed between the signal input circuit 'I and power supply circuit 33 of a radio receiver. Switch 26 may be used to either ground the antenna circuit direct by connecting it with terminal I9, or may be connected to terminal Il to utilize the full adjustable resistance afforded by the unit.

The results of the improved unit are more pronounced in circuits such as those illustrated in Figures 2 and 3 than in Figure 1, or where the resistance is adjusted directly across a single main aerial and the ground. Comparing the double contact switch member I3 with a single point contact, it will be seen that with the latter type of contact, for the greater portion of the time there is no veniering or tapering-off action from the one half of the resistor II, while with the spaced double contact member as disclosed herein, one half of the resistance is being shunted out while the other half is being gradually shunted in, and when the member I3 is rotated to either one of its extreme positions, or Where either one of the stops 23 or 24 contact pin 25, one of the contact heads I5 or I6 will be at a point approximately dead center, or will have divided the length of resistor II into two substantially equal parts. For example, Where an auxiliary aerial is used in conjunction with the main aerial as in Figure 2 and assuming that the member I3 is being rotated counterclockwise, the resistance in the main aerial line will be gradually increased while that in the auxiliary aerial line will be gradually reduced. By adjusting the resistance at a certain point, the signals may be finely acljusted in accordance with the characteristics of the particular set in which the device may be installed.

Regardless of the theory of operation of the improved control unit, I have found from practical experience that improved results are obtained with the two point spaced contact over the conventional single point contact type of control unit.

Another feature of importance is that the potentiometer resistance in devices of this kind is seldom uniform throughout the length thereof, and with the spaced two point contact type of unit as shown herein, the particular resistance used may be correlated with the particular circuit with which it may be installed. Thus one circuit, or the aerial circuit for example, may be adjusted on one side of the resistance while the grid-biasing resistance on the ground side of the circuit, for example, may be adjusted on the other side of the resistor.

A further point of advantage is that the two point switch arrangement is combined in one unit and therefore costs less to manufacture. Practical experience has also shown that the device has longer life than the conventional single point contact.

The stops 23 and 24 on the arms I3a and 13b of the rotatable contact plate or member I3 are preferably adjusted so that when either one contacts with the projection 25, the other contact will be at a point of dead center or will divide the resistance in two substantially equal parts,` as heretofore noted. It is also prefered to adjust these stops so that when they contact pin 25 there will be a slight space between the contact head and its adjacent terminal, so there will be sufficient resistance left as not to pass a current of any appreciable value as might occur should either contact I5 or IB directly engage either terminal I1 or I9. Thus in operation, the contacts I5 and I6 at no time directly ground either terminal of the resistance. The switch 26 may be used to selectively and directly ground either terminal I1 or I5 as shown in Figure 1, or said switch may be adjusted to a neutral position as shown in Figures 2 and 3.

It will be understood that the contacts I5 and I6 may be either the wiping or roller type and that certain other changes in design and arrangement of the parts of the improved unit may be adopted within the scope of the invention as defined by the appended claims.

I claim:

1. In a radio receiver having a signal input circuit, a power supply circuit and a common return such as a ground for said circuits, a resistance unit comprising a single unbroken resistance having opposed terminals connected respectively to said signal input circuit and said power supply circuit and a movably mounted contact member connected to said common return, said contact member having thereon a pair oi contacts engaging said resistance and spaced a predetermined distance apart so as to always render ineffective a section of the resistance therebetween, the contacts being positively connected for movement in unison.

2. In a radio receiver having a signal input circuit, a power supply circuit and a common return such as a ground for said circuits, a resistance unit comprising a single unbroken resistance having opposed terminals connected respectively to said signal input circuit and said power supply circuit and a pivotally mounted rotatable contact member connected to said common return, the contact member having contacts engaging said resistance and positively connected for movement in unison therealong, the contacts being spaced to render ineffective a portion of said resistance therebetween.

3. In a radio receiver having a signal input circuit, a power supply circuit and a common return such as a ground for such circuits, a resistance unit having a single unbroken resistance with opposed terminals connected respectively to said signal input circuit and said power supply circuit and an arcuate pivotally mounted rotatable contact plate connected to said common return, the contact plate having thereon contacts engaging said resistance and connected for positive movement in unison therealong, the spacing of said contacts being such as to render ineffective substantially one-third of the resistance therebetween.

4. In a radio receiver having a signal input circuit, a power supply circuit and a common ground for said circuits, a resistance unit having opposed terminals connected respectively to said signal input circuit and said power supply circuit and a contact member connected to said ground and having thereon a pair of contacts engaging y said resistance and spaced from each other so as to always render ineiective a portion of the reistance therebetween, the contacts being positively connected for movement in unison to vary the positions of contact with said resistance within certain limits, and a movable grounding switch to be selectively connected with either terminal oi said resistance or disconnected therefrom.

IRA O. BANKS. 

